81645569557 has 2 divisors, whose sum is σ = 81645569558. Its totient is φ = 81645569556.

The previous prime is 81645569539. The next prime is 81645569561. The reversal of 81645569557 is 75596554618.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 54363119281 + 27282450276 = 233159^2 + 165174^2 .

It is a cyclic number.

It is not a de Polignac number, because 81645569557 - 2²³ = 81637180949 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 81645569495 and 81645569504.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81642569557) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40822784778 + 40822784779.

It is an arithmetic number, because the mean of its divisors is an integer number (40822784779).

Almost surely, 2^81645569557 is an apocalyptic number.

It is an amenable number.

81645569557 is a deficient number, since it is larger than the sum of its proper divisors (1).

81645569557 is an equidigital number, since it uses as much as digits as its factorization.

81645569557 is an evil number, because the sum of its binary digits is even.

The product of its digits is 45360000, while the sum is 61.

The spelling of 81645569557 in words is "eighty-one billion, six hundred forty-five million, five hundred sixty-nine thousand, five hundred fifty-seven".